Traffic Grooming in Bidirectional

6 We study the minimization of ADMs (Add-Drop Multiplexers) in optical WDM bidirectional 7 rings considering symmetric shortest path routing and all-to-all unitary requests. We precisely for8 mulate the problem in terms of graph decompositions, and state a general lower bound for all the 9 values of the grooming factor C and N, the size of the ring. We first study exhaustively the cases 10 C = 1, C = 2, and C = 3, providing improved lower bounds, optimal constructions for several 11 infinite families, as well as asymptotically optimal constructions and approximations. We then study 12 the case C > 3, focusing specifically on the case C = k(k + 1)/2 for some k ≥ 1. We give optimal de13 compositions for several congruence classes of N using the existence of some combinatorial designs. 14 We conclude with a comparison of the cost functions in unidirectional and bidirectional WDM rings. 15 16